This invention relates to apparatus and methods of thermally processing a material such as a semiconductor substrate, and, in particular, to apparatus and methods for processing of a semiconductor substrate requiring precise measurement and control of the temperature over a wide range of temperatures. One example of such processing is rapid thermal processing (RTP), which is used for a number of fabrication processes, including rapid thermal annealing (RTA), rapid thermal cleaning (RTC), rapid thermal chemical vapor deposition (RTCVD), rapid thermal oxidation (RTO), and rapid thermal nitridation (RTN). In the particular application of CMOS gate dialectric formation by RTO or RTN, thickness, growth temperature, and uniformity of the gate dialectrics are critical parameters that influence the overall device performance and fabrication yield. At least some of these processes require that temperature across the substrate vary by less than a few degrees Celsius.
During thermal processing, precise measurement of the substrate temperature may be required at various stages of the processing, including such stages as heating or preheating of the substrate. During the preheating stage, the substrate is typically held on one or more lift pins while it is heated by one or more radiative heat sources. During this heating process, the temperature of the substrate must be accurately determined. This determination may be provided to a feedback controller to adjust the power of the radiative heat source(s), thereby optimizing the heating process.
Measurement of the substrate temperature is conducted by various means. At temperatures above approximately 300-325EC, pyrometers may be employed to measure the substrate temperature based on the radiation which is emitted by the substrate. At lower temperatures, the emission intensity from the substrate (within the wavelength range to which pyrometers are most sensitive) generally is insufficient for the pyrometers to accurately measure substrate temperature. Contact probes (e.g., thermocouples) are therefore used to monitor substrate temperature, at lower temperatures. Such direct temperature measurement techniques, however, are difficult to reliably implement because of various problems, including degradation of the contact probe and maintenance of a stable thermal contact between the probe and the substrate.
One particular method of measuring the substrate temperature, including measurements below temperatures of approximately 300-325EC, which typically occur during preheating, involves measuring the temperature through the lift pins which support the substrate during heating. These lift pins typically comprise a hollow body through which radiation is transmitted. One end of the hollow body is in contact with the substrate, while the other end is connected to a detection and/or processing system. Radiation emitted from the substrate passes through the hollow body, and is conveyed to the detection system. The intensity of the radiation at certain wavelengths is then measured, and the temperature is derived from that intensity. U.S. Pat. No. 6,151,446, which is incorporated herein by reference, describes such a method.
Such systems, however, still suffer from a lack of accuracy. The determination of the substrate temperature is highly dependent on the intensity of the radiation received by the detector. If the radiation received by the detector does not accurately represent the light emitted by the substrate, the determination of the substrate temperature will likewise be inaccurate. That situation can arise, for instance, if the lift pins do not fully or closely seat against the substrate. Gaps between the ends of the lift pins and the surface of the substrate can allow radiation emitted by the substrate to escape, or can allow other radiation, which was not emitted by the substrate, to enter the lift pin. Either case may result in inaccurate measurement of the substrate temperature.
A need therefore exists for a more accurate method and apparatus for measuring substrate temperature.
This invention is generally directed to method and apparatus for processing radiation emitted by a substrate. A lift pin is configured to convey radiation from the substrate to a measuring or processing device such as a pyrometer. One end of the lift pin comprises a contact surface configured to contact the substrate. The contact surface is flexibly connected so that the position and/or orientation of the contact surface may be adjusted to accommodate the surface of the substrate.
As used herein, the term substrate broadly refers to any object that is being processed in a thermal process chamber. Such substrates may include, for example, semiconductor wafers, flat panel displays, glass plates or disks, and plastic workpieces.
In one embodiment, the lift pin comprises a hollow member configured to convey radiation to a pyrometer or other receiving device. The lift pin further comprises a contact member flexibly connected to the hollow member. This connection may be a pivotal or rotatable connection, or may comprise any method of flexible connection known in the art. In one embodiment, the hollow member and the contact member are connected by a ball and socket joint. This flexible connection allows the contact member to seat against the adjoining portion of the substrate surface, improving the conveyance of radiation from the substrate to the pyrometer. One advantage of a ball and socket type connection is that such a connection can accommodate a central channel for transmitting radiation. Of course, the invention is not limited to lift pins that support the substrate; other types of pins or probes may be employed within the scope of the present invention.
Preferably, the invention is employed in a system for measuring substrate temperatures during thermal processing. As a substrate is radiatively heated, a contact member is in contact with the surface of the substrate. The contact member is flexibly mounted, allowing it to seat closely or snugly against the surface of the substrate. The contact member is connected to a hollow member. Radiation emitted from the substrate is conveyed past the contact member, through the hollow member, and to the pyrometer or other receiving device. The contact member and the hollow member are configured to provide the most efficient and accurate transmittal of radiation to the pyrometer. Further, gaps between the contact member and the substrate are reduced or eliminated by the flexible connection between the contact member and the hollow member, allowing the contact member to adjust to the angle of the substrate surface. In this way, radiation received by the pyrometer is conveyed directly from the substrate; losses or leakage outside of the lift pin are minimized or eliminated.
For a better understanding of these and other aspects of the present invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings.